Fixing Voids in Engineered Flooring

Q.A subcontractor glued down
4 1/2-inch-wide plank engineered flooring on a concrete
slab-on-grade using flooring adhesive applied with a
V-notch trowel. But the instructions on the bucket
indicated that a 1/4-inch square notched trowel should
have been used instead; consequently, the spread rate
was about 25 percent less than it should have been. Now
the floor has developed several ‘hollow spots'
where the flooring seems to be floating rather than
firmly glued to the substrate beneath. The sub says
he'll use a small drill and inject some adhesive into
the hollow spots, but the homeowners have misgivings
about this approach. What should I have the
subcontractor do to fix this?

A.Michael Purser, a
second-generation wood flooring contractor in
Atlanta, responds: While it's reasonable to
suppose that the trowel's spread rate has caused
the problem you describe, it's more likely that
this situation is the result of unevenness in the
concrete's surface.

Regardless of how much mastic is put down, if a
poured concrete slab has significant low or high
spots, these are probably the source of voids
between the flooring and the subfloor. The
engineered product is not going to stay in place
unless the surface is reasonably flat; if it isn't,
the flooring breaks free from the mastic. And in
this case, the flooring's 4 1/2-inch width would
only make the situation worse; flooring with a
thinner — and therefore more flexible
— profile would be a bit less likely to
separate from the glue.

Injecting glue into the affected areas is a very
common solution. Although some installers resort to
epoxy, DriTac (800/394-9310,
www.dritac.com) makes a repair
kit — consisting of an injection gun,
adhesive cartridges, mixing nozzles, applicator
tips, and drill bits — designed
specifically for this situation.

To use the kit, you start by drilling a pair of
small, 3/32-inch-diameter holes into the wood
flooring, preferably in a low-profile spot like a
head joint, a V-joint, or wherever there is
noticeable graining. One hole is used to deliver
the glue, and the other allows air to escape as the
glue is injected into the cavity (more holes may be
necessary for larger areas). The adhesive is
self-leveling, so after the cavity is completely
filled (you'll know because glue will start to come
out of the second hole), you can fill the holes
with a tapered dowel trimmed to fit and matching
putty.

According to the manufacturer, there's no need
to apply weight to bed the flooring in the new
adhesive, and the flooring can be used immediately
after repair.

This is not an unusual problem for engineered
flooring, and it's easily remedied. Your
subcontractor's solution is very typical and shows
that he has successfully dealt with this situation
before.